The sun occasionally releases significant amounts of charged particles during events known as coronal mass ejectas (“CMEs”). The charged particles released during CMEs include electrons, protons, and heavy ions. Each CME may last for about one or two days in the vicinity of earth, but their effects may linger for up to a week. Such proton and heavy ion radiation can cause cell damage to humans exposed to such radiation. Additionally, sensitive electronic components and other devices may be adversely affected by such radiation. Therefore, even though CMEs are relatively uncommon occurrences, the amounts of radiation they could potentially inflict upon a crew and equipment of a spacecraft suggests that consideration be given to shielding part or all of a spacecraft from such radiation. Similarly, comparable radiation protection may be desirable in other environments as well, such as habitats for celestial bodies such as the moon and Mars.
Shielding from proton and heavy ion radiation may generally be accomplished by either absorbing the particles or by deflecting the particles. To absorb the radiation, materials of a thickness sufficient for the amount of energy expected from the radiation, can be provided around an area that houses the crew and/or sensitive equipment during a CME. However, because of the significant amount of weight such a housing would require, the use of radiation absorbing material is not practical for space exploration and other applications. Additionally, the absorption of high energy particles may release a different form of radiation such as gamma rays and X-rays that pass through the shielding material and create other difficulties for the crew and/or equipment.
It may therefore be preferable to deflect the particles of radiation rather than absorb them. In order to deflect particles of radiation, active radiation shield devices have been proposed. An active radiation shield device may include one or more coils that extend about an area to be shielded, such as about a spacecraft or the like. By passing current through the coil(s) of the radiation shield device, a magnetic field may be generated that deflects particles of radiation that may otherwise impinge upon the spacecraft.
In order to facilitate the generation of the protective magnetic field, a radiation shield device may include coils formed of a superconductive material. During operation, the coils formed of the superconductive material must therefore be maintained at a temperature below its critical superconducting temperature onset level and as close to absolute zero as practical. As such, the coils formed of a superconductive material may be cooled to a temperature below its critical superconducting temperature onset level by electrical refrigeration units. However, the electrical refrigeration units may be relatively heavy and may consume a substantial amount of electrical power. In addition, the electrical refrigeration unit may require electrical power generation and distribution, which also disadvantageously adds to the overall weight of the system.
As it is often desirable to reduce the weight of a spacecraft, it may therefore be undesirable to include an electrical refrigeration unit and the associated electrical power generation distribution system in order to cool the coils formed of a superconducting material to a temperature near absolute zero. As such, radiation shield devices, including coils formed of a superconductive material, may alternatively immerse the coils in liquid helium, which lowers the temperature of the coils from an ambient temperature, such as about 23° C., to a temperature required for superconducting operations, such as −269° C., as a result of the boil-off vaporization of the liquid helium. Since the latent heat of the liquid helium is relatively low, however, an excessive amount of liquid helium, as measured in terms of the weight and volume of the liquid helium, may need to be boiled off in order to cool the coils. As such, a substantial quantity of liquid helium may be required to be provided in order to sufficiently cool the coils formed of a superconductive material, thereby disadvantageously increasing the weight of the spacecraft or the like. Additionally, the liquid helium must be stored onboard the spacecraft and may consume a portion of the interior volume of the spacecraft that could otherwise be utilized for other purposes, such as for the crew and/or instrumentation.
In order to conserve power in an instance in which the cooling of the superconductive coils is provided by an electrical refrigeration unit or to limit the boil off of liquid helium in an instance in which the cooling of the superconductive coils is provided by liquid helium, the superconductive coils may not be maintained at the temperature required for superconducting operations, such as −269° C., at all times throughout the mission. Instead, the superconductive coils may be maintained at a nominal temperature that is greater than that required for superconductive operations. The spacecraft may be configured, however, to detect a CME or the approach of other high energy particles and, once detected, may be further configured to initiate cooling of the superconductive coils, such as by an electrical refrigeration unit or liquid helium, so as to bring the coils to a temperature required for superconducting operations prior to exposure to the CME or other high energy particles. However, this approach by which the superconductive coils are in a state of readiness during only selected time periods, such as only in response to the detection of a CME or other high energy particles, may limit overall mission availability and reliability.